JPH051746B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to an optical information recording medium on which information can be recorded and reproduced using semiconductor laser light, and a method for manufacturing the same. (Prior Art) Optical disk memories, which record and reproduce information on a medium using laser light, have excellent characteristics as large-capacity recording devices because of their high recording density. Tantalum and lead were first used as materials for this optical recording medium {Science
154, 1550, 1966)}. Since then, various materials have been used, but chalcogen elements such as tellurium or their compounds are often used (Japanese Patent Publication No. 47-1982).
In particular, tellurium-selenium alloys are often used (Japanese Patent Publication No. 54-41902, Japanese Patent Publication No. 57-7919, Japanese Patent Publication No. 57-56058). An example of an optical recording medium using this tellurium-selenium alloy as an optical recording layer has a structure as shown in FIG. That is, a recording layer 21 made of a tellurium-selenium alloy is provided adjacent to the substrate 1. The recording laser beam passes through the substrate 1 to the recording layer 2.
1 is condensed and irradiated to form a pit 22. The substrate 1 is made of synthetic resin such as polycarbonate, polyolefin, polymethylpentene, acrylic, or epoxy resin, or glass. Usually, the substrate 1 is made of a material such that pits are recorded concentrically or spirally at regular intervals with high precision. A guide groove is provided. When light enters a groove with a width similar to the diameter of the laser beam, the light is diffracted, and as the beam center shifts from the groove, the spatial distribution of the intensity of the diffracted light changes.This is detected and the laser beam is directed to the center of the groove. The servo system is configured as follows. The width of the groove is usually
The depth of the groove is set in the range of 1/20 to 1/4 of the wavelength of the laser used. A servo system is similarly configured for condensing light. Information is read by irradiating a laser beam with a weaker power than during recording so as to pass over the pits, and detecting changes in reflectance due to the presence or absence of pits. In recent years, in order to downsize recording devices, semiconductor lasers have been used as laser light sources. Semiconductor lasers have an oscillation wavelength of around 8000 Å, and tellurium-selenium alloys are relatively well suited to this wavelength range, and can provide moderate reflectance and moderate absorption {Fijica Status Solidai, 7 , 189,
1964 (phys.stat.sol. 7 , 189, 1964)}. (Problems to be Solved by the Invention) However, there has been no tellurium-selenium alloy film that has good weather resistance, can provide recording and reproduction signals of good quality, and is suitable for semiconductor laser recording. An object of the present invention is to provide an optical information recording medium that has good weather resistance, good signal quality, and is suitable for semiconductor laser recording, and a method for manufacturing the same. (Means for Solving Problems) The optical information recording medium of the present invention is an optical information recording medium in which a recording layer is provided on one or both sides of a substrate, and information is recorded and read by a semiconductor laser beam. The method for producing an optical information recording medium of the present invention, which is characterized by containing nitrogen, selenium, and tellurium as main components, provides a recording layer on one or both sides of a substrate, and records and reads information using a semiconductor laser beam. The method for manufacturing an optical information recording medium is characterized in that selenium and tellurium or an alloy of selenium and tellurium is used as a target and is formed on the substrate by sputtering in a mixed gas of an inert gas and nitrogen gas. The thickness of the recording layer whose main components are nitrogen, selenium, and tellurium is 180 mm from the viewpoint of recording and reproducing characteristics.
A range of Å to 400 Å is particularly desirable. The content of selenium is particularly preferably 10% or more and 30% or less in atomic % from the viewpoint of recording/reproducing characteristics, weather resistance, and unrecorded noise.
The nitrogen content is particularly preferably 2% or more and 10% or less in atomic percent from the viewpoint of recording/reproducing characteristics and weather resistance. The optimum nitrogen gas partial pressure of the sputter gas depends on the sputter gas flow rate. From the viewpoint of production stability, it is desirable to carry out the sputtering with a sufficiently large flow rate of the sputtering gas. Under these conditions, the nitrogen gas partial pressure is 1
Less than % is desirable. (Function) The reason why the recording layer of the present invention whose main components are nitrogen, selenium, and tellurium is more sensitive than the conventional tellurium-selenium alloy is that the explosive properties of tellurium nitride and selenium nitride This is because the temperature of the recording layer, which causes the formation of small holes and the expansion of the holes due to surface tension, is lowered. Compared to the tellurium nitrogen recording layer, the recording layer of the present invention has higher sensitivity by adding selenium to lower the melting point of the entire system. The nitrogen content in the recording layer should not be too low since the effects of the present invention cannot be obtained, but it should not be too large. If there is too much nitrogen, the film will have almost no absorption at the semiconductor laser wavelength (around 800 nm), making it impossible to record with high sensitivity. For this purpose, it is particularly desirable that the nitrogen content be 10% or less in atomic percent. The amount of nitrogen in the recording layer is controlled mainly by the nitrogen gas partial pressure of the sputtering gas and the sputtering gas flow rate. In order to stably manufacture optical information recording media with good mass productivity, it is necessary to perform sputtering with a sufficiently large sputtering gas flow rate. Under such conditions, good recording and reproducing characteristics can be obtained with a nitrogen gas partial pressure of less than 1%. (Example) Examples of the present invention will be described below. A polycarbonate resin disk substrate with a guide groove having an inner diameter of 15 mm, an outer diameter of 130 mm, and a thickness of 1.2 mm, which had been annealed at 100° C. for 2 hours, was placed in a magnetron sputtering device equipped with a 13.56 MHz high-frequency power source, and the air was evacuated. After evacuation to below 1×10 ^-6 Torr, argon gas and nitrogen gas were introduced to bring the pressure to 1×10 ^-2 Torr.
At this time, the nitrogen gas partial pressure was 0.26%, and the nitrogen gas flow rate was 0.30 SCCM. By sputtering an 8-inch target of a sintered body of tellurium selenium alloy with a ratio of 80:20 at % by using this mixed gas at an input power of 100 W, a film about 220 Å thick was formed on the disk substrate. Thereafter, the optical information recording medium was manufactured by storing the medium for 12 hours at a temperature of 85° C. and a relative humidity of 90% to crystallize the tellurium-selenium-nitrogen layer. Analysis of this recording layer revealed that the atomic ratio of tellurium, selenium, and nitrogen was approximately 77:19:4. When we measured the reflectance of the land portion of this optical disk at a wavelength of 830 nm, it was approximately 35.
It was %. Semiconductor laser light with a wavelength of 830 nm is incident through the substrate and focused to about 1.6 umφ on the recording layer.
Recording was performed on the land portion under the conditions of a medium linear velocity of 5.65 m/sec, a recording frequency of 3.77 MHz, a recording pulse width of 70 nsec, and a recording power of 7.5 mW, and reproduction was performed at a constant power of 0.7 mW. The carrier-to-noise ratio (C/N) with a bandwidth of 30 kHz was stably obtained at a good value of 50 dB, and the bit error rate (BER) was also stably obtained in the 10 ^-6 range. Even when this optical disk was stored in an environment of 60°C and 90°C for 1000 hours, all characteristics such as reflectance, C/N, recording sensitivity, and BER did not change. Even after storing for 3000 hours in a harsh high temperature and high humidity environment of 80℃ and 90%, there were no practical problems in recording sensitivity or BER. Also, 85℃90
There were no practical problems with recording sensitivity or BER even after storage for 2,000 hours in an even harsher high-temperature, high-humidity environment. From the above, it was confirmed that the optical recording medium of the present invention has high sensitivity and good signal quality, has excellent weather resistance, and is suitable for recording with a small semiconductor laser. Table 1 shows the recording and reproducing characteristics of the optical information recording medium when the thickness of the recording layer was changed. The thinner the recording layer is, the higher the sensitivity will be, but the rim formed around the pit will be discontinuous and the noise will increase after recording, and the reflectance will decrease and the carrier will become smaller, so it is difficult to obtain a good C/N. The value is no longer available. On the other hand, if the recording film is made thicker, the recording sensitivity will deteriorate and the amount of recording layer material that will be melted and removed from the irradiated area will increase, resulting in uneven formation of the rim and C/N.
decreased. Therefore, the thickness of the recording layer is
The range from 180 Å to 400 Å is particularly good.

[Table] The effect of selenium content was tested by changing the composition of the sputtering target. The ratio of tellurium to selenium in the target composition was approximately equal to the ratio of tellurium to selenium in the film obtained by sputtering. Table 2 shows the media characteristics when the selenium content was changed. Films with too little selenium content as shown in Table 2 had a problem of corrosion when stored in a high temperature, high humidity environment for a long time. On the other hand, if the film contains too much selenium, unevenness on the order of microns will occur and unrecorded noise will become large, which is a problem. Therefore, a particularly good selenium content was 10% or more and 30% or less in atomic %.

[Table] Table 3 shows the media characteristics when the nitrogen content was changed. Films with too little nitrogen content had poor recording sensitivity. Further, it was not possible to record uniformly over one circumference of the track, and some pits were observed to be missing. Therefore, the BER was very poor and the C/N was also poor. Good C/N as you increase the recording power
was obtained (this means that when many tracks were recorded, there were also tracks with good C/N values,
However, if the recording power was further increased, the tracking servo would malfunction, and the margin of recording power was extremely narrow, which was a problem. Further, even when a good C/N was obtained, the BER was poor and partial pits were missing. The reason for this is that although the tellurium-selenium film has a low melting point, it is difficult to form small holes in the irradiated melted portion, making it difficult to open pits, and therefore, a large recording power is required to form pits. In addition, in order to put in a large recording power,
The area of the melted part increases, and once the pit opens, it becomes a large pit, making the tracking servo more likely to malfunction. In the optical information recording medium of the present invention in which tellurium and selenium are partially nitrided, due to the explosive nature of tellurium nitride and selenium nitride,
Since small holes are easily and stably formed in the irradiated melted part, the recording sensitivity is good, and since no pits are missing, the BER is also good. Furthermore, since the pit opens without melting over a large area, the pit is not very large and there is no malfunction of the tracking servo. With a film containing too much nitrogen, the surface properties of the film deteriorated and the rim around the pits was not formed neatly, resulting in increased noise after recording. Therefore, a good C/N value could not be obtained. When the nitrogen content further increased, the film became a film that had absorption at the argon laser wavelength, but almost no absorption at the semiconductor laser wavelength of around 800 nm. Therefore, the nitrogen content is 2% or more and 10% in atomic percent.
The following are particularly desirable.

[Table] The amount of nitrogen in the recording layer was controlled mainly by the nitrogen gas partial pressure of the sputtering gas and the sputtering gas flow rate. At the beginning of the experiment, the sputtering gas flow rate was a small value of 1.4 SCCM, so a film with a nitrogen content of 4 at % was obtained at a nitrogen gas partial pressure of 4%. However, it has been found that the medium characteristic values vary greatly due to subtle differences in the internal state of the chamber of the sputtering device. However, it was found that a recording film could be stably produced by forming the film at a sputtering gas flow rate of 20 SCCM or more. Under these conditions, good recording and reproducing characteristics were stably obtained with a nitrogen gas partial pressure of less than 1%. (Effects of the Invention) As is clear from the above examples, the optical information recording medium of the present invention has good weather resistance, good signal quality, and is suitable for semiconductor laser recording.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of an optical information recording medium. 1 is a substrate, 21 is a recording layer, and 22 is a pit.

Claims (1)

[Claims] 1. An optical information recording medium in which a recording layer is provided on one or both sides of a substrate, and information is recorded and read by semiconductor laser light, wherein the recording layer contains nitrogen, selenium, and tellurium as main components. An optical information recording medium characterized by: 2. In a method for manufacturing an optical information recording medium in which a recording layer is provided on one or both sides of a substrate and information is recorded and read using a semiconductor laser beam, selenium and tellurium or an alloy of selenium and tellurium are targeted, and an inert gas and 1. A method for manufacturing an optical information recording medium, comprising forming the medium on the substrate by a sputtering method in a mixed gas of nitrogen gas.